Generally, internal combustion engines require the pistons to be moving before ignition can commence. Typically, this means that the engine must be set in motion by some external force before the engine can power itself via combustion of fuel. Most vehicles employ an electric starter to set the engine in motion, thereby allowing ignition to take place.
An electric starter motor is often used to crank internal combustion engines prior to ignition. Typically, the electric starter consists of three main assemblies: 1) the solenoid switch that ensures axial movement of the plunger within the electrical coils of the switch, and, therefore, the subsequent engagement and disengagement of a pinion into a ring gear through an engagement lever, and also establishing and breaking of the electrical contacts, which enables transmission of electric energy from the battery to the electric motor part of the starter; 2) a DC electric motor, which transform electrical power into the mechanical rotating power that is required to crank the internal combustion engine; and 3) a mechanical transmitter which consists of a reduction gear, clutch, and a pinion, and is used to transmit the rotating power from the electrical motor to the internal combustion engine.
A typical starter for a vehicle may include a DC electric motor with a solenoid switch that is activated upon the closing of an ignition switch. When a driver turns an ignition key or presses a start button that closes the ignition switch, an electrical current is supplied from the battery to the solenoid windings. Typically, this causes a drive pinion on the starter driveshaft to mesh with a ring gear on the flywheel of the engine. The solenoid assembly, which has an electrical winding, electrical terminals, and high-current contacts, acts to close the high-current contacts for the starter's DC electric motor after the drive pinion engages the ring gear, thus connecting the battery to the electric motor and causing the electric motor to turn. The meshing of the pinion to the flywheel ring gear means that the rotating DC electric motor causes the vehicle engine to rotate as well. Generally, after the engine starts, the ignition switch opens, and a return spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter's electric motor stops.
Occasionally, the switching of the starter motor current on and off results in a partial welding or fusing of the high-current contacts and the electrical terminals due to electrical arcing between the high-current contacts and the contact plate. Typically, the solenoid assembly return spring has enough force to mechanically break this partial fusing of contact and terminal. However, occasionally, the return spring force is insufficient, and the solenoid's high-current contacts can become welded in the closed position to a contact plate. This causes the starter's DC electric motor to maintain its connection to the vehicle battery even after the engine is running, and the starter will remain energized after the vehicle operator has released the ignition switch. Consequently, the starter motor will continue to run even after the vehicle engine is running on its own and the pinion has disengaged from the ring gear. As a result of the welded contact plate and terminals, it is possible that the starter motor could continue to run after the engine is turned off. In this case, the continuous usage of electrical energy by the starter motor may cause the battery's charge to be depleted prematurely. In any case, continuous operation of the starter motor caused by welded contact plate and terminals, will likely result in the overheating and premature failure of the starter motor, leading to increased maintenance costs for the vehicle owner and a potential for premature replacement of the affected components.
It would therefore be desirable to have a solenoid assembly with a mechanism for reducing the likelihood of high-current contact plate becoming welded to the electrical terminals. Embodiments of the invention provide such a solenoid assembly. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.